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U. S. DEPAR I'MIA I' I )l AGRICULTURE 
BUREAU OF WTOMOLOQT CIRCULAR Ho. 154. 

L. O. HOWARD. Eniomologirt *nd Clurf of Burc»u. 



THE LEAF BLISTEB .MITK. 



A. L. QUAINTANCE, 






U V - 1 1 , 




BUREAU OF ENTOMOLOGY. 

L. O. Howabd, Entomologist and Chief of Bureau. 

C. L. Mablatt, Entomologist and Acting Chief in Absence of Chief. 

B. s. Clifton, Executive Issistant. 

W. F. Tastet, chief Clerk. 

F. II. Chittenden, in charge of truck crop andstqred product insect investigations. 

A. D. Hopkins, in charge of forest insect investigations. 

W. I>. IIixii u. in charge of -southern field crop insect investigations. 

F. M. Websteb, in charge of <■< n<n and forage insect investigations. 

A. L. Quaintance, in charge of deciduous fruit insect investigations. 

E. V. Phillips, in charge of bee culture. 

D. M. Rogers, in charge of preventing spread of moths. fit id work. 

Roi.la P. Cubrie, in charge of editorial work. 

Mabex Oolcord, in charge of library, 

Decidvois Fbuit [nsect Investigations. 

A. I,. Quaintance, in charge. 

Fred Johnson, S. W. Foster, P. R. Jones, F. E. Brooks. A. (;. IIa.mmak. K. \v. 

Scott, 11. L. Novgaret, It. A. Ctjshman, L. L. Scott. J. B. Gill, A. ('. Bakes, 

W. M. Davidson, E. B. Blakeslee, W. B. Wood. E. II. Stegleb, F. L. Si.ma.n- 

ton, entomological assistants. 
J. F. Zimmeb, X. S. Abbott, YV. H. Sill, cntotiwlogical assistants, employed in 

enforcement of insecticide act, 1910. 
ii 



: 



Crculah No. 154. 



United States Department of Agriculture, 

BUREAU OF ENTOMOLOGY. 
L. O. HOWARD, Entomologist and Chief of Bureau. 



THE LEAF BLISTER Mill.. 

{Briophyet pyri Pngenstecher > 

i:.\ a. I. iii \in i \m i . 
In Charge of Deciduous Fruit Insect Investigations. 

INTHODU" [TON. 

Leaf blister mites are among the smallest <>f animal forms which 
attack horticultural crops. These minute creatures, only one one- 
hundred-and-fiftieth of an inch in length, are invisible to the un- 
aided eye, and m> seen under a good hand lens appear a- the merest 
-peck. Although the mites themselves are probably unfamiliar to 
most ofchardists, their work is well known, to pear growers and 
apple growers, in the reddish or greenish pimples <>r blisterlike spots 
to Ik- noted in early spring on the young foliage of these plant-. 
Later these blisters become brown and dead, spotting and blotching 
the leaves, the injury resembling that due to leaf-spot fungi or from 
-I rays, with which injury, in fact, the work of this mite i- frequently 
confused. When the creatures are abundanl the foliage may be 
almost covered with the blisters or l.p.w n -pot-, and the usefulness of 
the leave- to the tree i- thus greatly impaired. Foliage severely 
injured will fall prematurely, retarding the development of the fruit 
and in extreme cases much id' the crop will fall to the ground. I S 

fig. 1.) 

The leaf blister mite i- not an insect, hut belongs to that class of 
animal- containing the spiders, scorpions, daddylonglegs, etc. and 
to the order Acarina, represented by such well-known form- a- the 
scah mite of sheep, the cattle tick, and the red spider. It- family, 
the Eriophyidae (Phytoptidse), contain- numerous species, all of 
which are plant feeders, attacking principally the hud- and lea 
Several members of the family are of much economic importance. 
ntie Landois infests vinifera varieties of grapes in por- 

1 



Z THK LEAF BLISTEB MITE. 

(ions of Europe and in California, producing the so-called " erinose " 
of the vine. Eriophyea padi Nalepa (=1?. prurd-crumena Walsh) 
is the cause of the nail-like galls sometimes found on the leaves of 
plum. (Typhlodrom/us) PhyUocoptea oleivorus Ashmead infests the 
fruit and foliage of the orange, producing a russeted condition. 
PhyUocoptea eomutus Banks feeds upon the upper surface of the 
leaves of the peach, so injuring them as to give the foliage a silvery 
sheen. PhyUocoptes sclilecldendali Xalepa occurs on the foliage of 
the apple, and in Montana very important injuries have been at- 
tributed to it. 







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Fig. 1. — Apple leaves injured by the leaf blister mite (Brtophyea i>>hi). (Original.) 
ORIGIN AND DISTRIBUTION. 



The mite is not native to the United States and was probably in- 
troduced at an early period, presumably from Europe on nursery 
stock, buds, or scions. It was first recorded in the United States by 
Townend Glover, in 1872, and since that date has made its appear- 
ance in the principal pear-growing regions of the United States and 
Canada. It is known to occur in portions of Europe, in England. 
Russia, and Tasmania, and is probably present in other fruit-growing 
regions of the world, being at the present time a truly cosmopolitan 
pest. 



i 111 ii \i 1:1.1-- 1 11; Miii. 



CHAHA< 111: IJ] INJURE \ M> DESTRl't I l\ 1 \ I --. 

The mile-. pass the winter on the trees, under the bud scales, and 
attack ilic leaves as soon a- these begin to «push oul in the Bpring. 
They bore -mall hole-, from the underside t" the interior '»f the leaf, 
where they deposit their eggs, and with their progeny feed upon tin' 
tender cells of tin 1 leaf substance. Their activities within tin- leaf 
tissues very quickly resull in the developmen! of galls or swellii 
These an- at (i 1-- 1 -mall, pimple like eruptions, especially evident on 
the upper surface of young leaves, whitish in color on the apple, 
but usually with a reddish t inge 

on the pear. The spots 

increase in size, the largest be- 
coming a- much as one-eighth of 
an inch in diameter. On pear 
leave- the -pot-, as a rule, be- 
come re.I. often brilliantly col- 
ored a- they grow, whereas on 
apple this reddish coloring i- ab- 
sent or faint. ( )n the underside 

of the leaf the oralis are whitish and blisterlike, not differing much 
from the general color of the leaf surface. Later they turn brownish 

or black, due to the death of the injured leaf cell-, lo-e much of their 

thickness, and some may become somi what shrunken. Figure 2 illus- 
trates a gall on pear leaf a- seen in cross-section, the normal structure 
being shown at //..• <> i- tin' opening to the interior of the gall and < 
designates eggs of the mite. A cro — ection of one of the dried-up 
galls i- shown in figure 3. 




i"i.. 2 1 :if null. In cr oss section, of leaf 
blister mlti nlng ->f sail : ■ 

• if miii'; 11. normal itruclure of leaf. 
1 a ft it Boraner | 




Fig. ". — SectloD of leaf, showing structure of gall of ''l i-t.-r mite In autumn: <;. OaU; o. 
opening of gall' (After Comstock.) 

On pear, the galls occur more along each side of the midrib of the 
leaf and on apple at the base of, and along the margins of the leaf. 
When numerous, however, the spots will merge together, forming 
large patches or hands of variable size, often involving most of the 
leaf. When thus abundant the leaves may become more or less rup- 
tured and wrinkled, and in the case of the apple the margins may 
curl up. showing the underside. Leaves badly infested are likely 
to fall prematurely, resulting al-o in the dropping of the fruit from 
clusters with wor-t injured foliage. The fruit and fruit --tenis of 
both apple and pear are al-o attacked, the light-colored pimple- 



4 THE LEAF BUSTER MITE. 

occurring mostly around the calyx end of the fruit and resulting in 
no material injury. The injury to the fruit-stems is noticeable as 
irregular thickenings, and when severe may cause some of the fruit 
to fall, although loss frofn this source, even in worst infested orchards, 
will not be great. 

FOOD PLANTS. 

Pear and apple are the more common food plants of the blister 
mite, though other plants are attacked. Dr. Nalepa records this 
species from foliage on the white lx»am tree (Sorljus aria Crantz). 
the European mountain ash (Sorhux niii-ujmria L.). the wild-service 
tree (Sorbus torrninalis Crantz), the service berry (Amelanchier 
vulgaris Monch.), and the common cotoneaster (Cotoneaster vulgaris 
Lindl.). 

According to Parrott the mites have been found on over 250 vari- 
eties of apples, injury being severe on some well-known commercial 
sorts, as Ben Davis. King, Baldwin, Rhode Island Greening, and at 
the agricultural experiment station at Geneva, X. Y.. the \Villiams 
Favorite was noted to be especially subject to attack, the trees having 
been prematurely defoliated for two successive seasons. 

DESCRIPTION AND HABITS. 

The general appearance of the blister mite is shown in figure 4 
in dorsal and ventral views. The mite is microscopic in size, measuring 
on the average about one one-hundred-and-fiftieth inch in length, 
whitish in color, a few individuals pinkish. The abdomen slopes 
gradually toward the posterior end and is numerously ringed. There 
are only two pairs of legs, and these and the body bear setae, which 
from their character and location are of importance in the deter- 
mination of species in this group, as are also the number and charac- 
ter of rings on the abdomen. The young, except in size, bear a gen- 
eral likeness to the adults, and the eggs, though proportionately 
large as compared in size with the parent, are only 46 microns 
through the greater diameter. These are whitish, translucent, with 
rounded ends, and are deposited in the interior of the galls (see fig. 2). 
The resulting larvae feed upon the cellular leaf substance, working 
out in various directions, though they are not especially active. 

The mites are to be found on the foliage from their appearance 
in spring until fall, and several generations are evidently produced 
in a season. Hibernation occurs under the bud scales, the mites often 
congregating in colonies of 50 or more. They become active in the 
spring often before the buds burst, congregating around the base of 
hud scales, where they feed, many molting at this time. "With the 
bursting of the buds and the pushing out of the tender leaves, these 
are attacked and the characteristic blisterlike spots soon develop. 



I ill i.l \r BLIS III: MM E. 



Notwithstanding the minute size of these creatures, they fall prey 
in considerable numbers, as observed by Prof. Parrotl in Nev "> nrl, 
State, to the attack of a mite ' N - itu pomi Parrotl i which he thinks 
materially assists in reducing their numbers. 



M I i Hi >n> {)] CONTHOI 



The leaf blister mite will yield to thorough treatment with kero- 
sene emulsion, miscible oils, i>r Lime-sulphur washes. The d 





er mite [BHophj/m pyri) : i. Dona] vi.'w: _•. rentral rlew. QreaUj 
enlarged i After Nal< p 

these sprays, as for the Sun Jose scale, should also protect orchards 
from important injury from the mites. When it -;irv to 

spray for the mites alone, and in cases of severe infestation, as has 
been notfil in apple orchards in New York State, two treatments 
have been recommended l>y Parrott, using standard kerosene emul- 
sion diluted with ."» parts of water. One application should be given 
in late fall as soon as most of the leave- have fallen and another the 
following spring before the trees put out foliage. If lM>th the fall 
and spring application- are uot practicable, the preference should be 



UNIVERSITY OF FLORIDA 



b Tin: LEA* blister 1 3 1262 09216 5959 

given to fall treatment. At this time many of the mites have not yel 
gQne to the bud scales, hut occur in the pubescence of the young 
wood and are hence more easily killed. 

Lime-sulphur washes arc excellent treatment- for these mites and 
their employment is perhaps preferable as avoiding danger of injury 
to fruit buds by the oil sprays. If a lime-sulphur wash is employed, 
it should be applied with great thoroughness, completely coating the 
tree so thai when spraying is finished the tree will appear as if 
whitewashed. The homemade wash, according to the old formula, 
lime 20 pounds, sulphur 15 pounds, and water to make 50 galL 
will be quite effective; or the homemade or commercial concentrate 
may he used. The former may be made according to the formula. 
lime 50 pounds, sulphur LOO pounds, and water to make 50 gallon-. 
When thus prepared the concentrate should be used at the rate of one 
part to 9 or 10 parts of water. Applications of these washes may 
also be made in the fall as described for kerosene emulsion and in 
the spring, and if only one treatment is to he given the spring appli- 
cation is preferable, as it takes the place of the first application of 
a fungicide for apple scab. When the mite is quite troublesome both 
fall and spring treatments would insure its control more quickly and 
completely. 

On the pear the mites may be kept reduced to an important extent 
simply by searching out in the spring branches bearing worst infested 
leaves, pruning these oil' and burning them, or sprays may be em- 
ployed exactly as indicated for the apple, if this is considered 
necessary. 

Except in cases of serious infestation special spraying for the 
Mister mite will not be necessary. As to whether or not it i- advisa- 
ble to spray, the orchardists will have to decide after determining as 
exactly as is possible the amount of injury being done by the mites, 
and care should be taken not to confound with it- injury that which 
has resulted from fungicidal or Paris-green sprays, and from leaf- 
spot (li-ease-. 

Approved : 

James Wilson, 

Secrt tary of . Vgriculture. 
Washington, I). C, April /<>. 1912. 



ADDITIONAL COPIES of this publication 
XV may be procured from the SUPERINTEND- 
ENT of Documents, Government Printing 
Office, Washington, D. C. , at ."> cents per copy